The fact is that the difference between the former Yugoslavia and the Ukraine is minimal. In both cases the same magnitude of heterogeneity. Both had or have the same internal political distance between pro-Western and anti-Western political forces. Like Yugoslavia the Ukraine has a similar mixture of ethnicities and religions: Catholics, quasi-Catholics, Ukrainian Orthodox,Russian Orthodox and Moslems. And what may be most important: In both countries there was or is a division line between two different cultures or civilizations. In Yugoslavia Oriental vs Western, in the Ukraine Russian vs Western.
In Yugoslavia NATO did not hessitate to assist the division along such lines. Of course the Ukrainians have not commited the same genocide and ethnic cleansing as the Serbs, but still the divisions in this country are strong enough to allow a splitting up.
The Western powers should let Russia aid Crimea to independence from the Ukraine. This peninsula has always been Russian and was only by accident given to the Ukraine in Soviet times. It has the only major Russian naval base to the South. What would the Americans do if a left-wing Ecotopia in the west broke away with all American naval bases along the Pacific coast?
Russia has already been pressed too much with the breakup of the USSR loosing large areas inhabited by Russians.
The West would be well advised not to press Russia further. Let it get Crimea. Pressed more there is a danger of a real new Cold War. A Russia with its back against the wall could become very strong in a desperate defensive resistance.
And Russia would be well advised to be satisfied with Crimea. Taking more would give uncontrollable international tensions and also reduce the proportion of Russian-speakers in the Ukraine and thus reduce the chance of Russia later getting more control over the rest of the Ukraine as the mood here changes for economic and cultural reasons.